TOWARDS THE SELECTIVE ACYLATION OF SECONDARY HYDROXYL-GROUPS OF CARBOHYDRATES USING OXIME ESTERS IN AN ENZYME-CATALYZED PROCESS

A lipase from Candida antarctica was used for the regioselective acylation and alkoxycarbonylation of the primary hydroxyl group of 2-deoxy-D-arabino-hexopyranose (1) and 2-deoxy-D-lyxo-hexopyranose (2) using oxime esters as acylating agents. Both, pyridine and 1,4-dioxane were used as solvents in the acylation process, but only 1,4-dioxane was effective for the alkyloxycarbonylation. A lipase from Pseudomonas cepacia catalyzed also the regioselective acylation of the primary hydroxyl group of 1 and 2 when 1,4-dioxane was used as solvent. Moreover, this lipase was a suitable biocatalyst for the acylation of the secondary HO-3 of 6-O(benzyloxy)carbonyl derivatives of 2-deoxy-D-hexoses. Subsequent deprotection of the primary hydroxyl group through catalytic hydrogenation readily afforded the 3-O-acyl derivatives of 1 and 2. A study of the regioselective acylation and alkyloxycarbonylation of 1,6-anhydro-beta-D-glucopyranose by the aforementioned lipase is also reported.